Amplifier circuits



Jan. 10, 1928. I 1,655,557" R. C. MATHES AIPLIFIER CIRCUITS Filed Nov. 7, 1919:.

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UNITED STATES PATENTOFFICE.

Bonn-Br o; rams, or new Yonx, n. 1., ABBIGNOB 'ro wns'rnmt morale courm, mconrom'rnn, or new YORK, n. 1., A 'conrona'rron or new Yonx.

mm omourrs.

Application fled Iovenber 1, me. man Io. seam.

This invention relates to amplifier circuits and has for an ob'ect the provision of means for increasing t e amount of amplification that may be secured from an amplifier, particularly of the audion type.

As is Well' known in the art, a vacuum tube of the three-electrode type may be'employed for amplifying currents smc'e'iznly currents impressed on thecontrol electr e of the tube will appear in 'amplified form in the output circuit well-known that the output and input circuits of the tube may be associated so that a pontion of the output energy may be fed back into the p thereby greatl increasing the degree of amplification'wh1ch may be obtained from a tube of a giventype.- Such arrangements applied to a single tube have, in the past,

given greatly increased amplification: at a single or very narrow range of frequencies resultingin anamplifier of a highly selective character. .This 'invention contemplates associating the output; and input circuits through a mutual irnpedance' or translator of uniform efiicieney over abroad of ifrequencics, thereby greatly brrmdcn one field of usefulness of such devices nus us cult is secured preferably it one winding of which is placed in r ing in the input circuit the that; o 1 the indings being shunted by a lit is found, furthermornfihet it is necesssry to limit the am -cu nt oif energy trans ferred back in under to prevent the genera Que andt'ion of undemped oscillations. the preferred Way of limiting the degree or feed back is to make resistance a est-he increased amplification clue to feed back will be Zero when this resistance is'zero, and a maximum below the critical velue which produces sing- This invention be better understood by reference to the *Eollowing detailed description taken connection with the ac companying. drawrngs; 1n whlch Fig. 1 represents the preferred form of the invention;

Fig. 2 represents amplification curves of a vacuum tube amplifier; andFig. 3 represents this invention applied to a two stage amplifier set.

Referring to Figl 1, 4 is a vacuum tube anode 5 7a cathode 6 a conof the tube. It is also input circuit to be reamplified,

when adjusted jmt trol electrode 7. Heating current for the cathode 6 1s supplied by a-batter 9. Ourrent for the output circuit of the tube is supplied by source of voltage 10. 12 is a source of currents to bev amplified which 1s associated 'with the input circ'uitof. the amplifier bymeansofiz transformer 13. A

- suitable receiving device 15 'is associated with the output circuit of the amplifier by' means of a transformer 16 so that the device 15 will receive signals from source 12'that have been amplified by'tube In -order toincreaSethe amount of amplification'produced by tube 4, means are provided for feeding back to the input circuitof the tubea portion of the amplified energy in the tubes foutput circuit.- This may e accomplished by inserting" the primary' winding 18 offs transformer in the output circuit of the tube and by inserting the secondary 19 of the transformer in the input circuit of the tube. A're'sistance 20 is shunted around the Winding 19 of the feed-back transformer'in order togive the transformer practically uniform translating eficiency over a broad range of -freuguenoies. This-resistance is' further made adjustable so that the degree of feed. back may be con trolled to any desired degree and thereby prevent the tube from singing orgenersting a ternstrng current -a condition that would be. undesirable in the ease of a vacuum tube used, to repeat signals without distortion.

is" desirable that the value of" this resistance 20 should be adjusted so that it is just below the value which will permit the tube to sing. With this adjustment the maximum amount of amplification is secured from the tube, while still preventing the tube fiom singing.

" liig. 2 illustratesamplification curves for a; vacuum tube in which the ordinates repre sent the'degree of amplification obtained for an incoming impulse of a givenstrength and the ebscissas represent various values of he quency the impulse may have. Curve 22 represents the amount 0 amplification that ma obtained from a vacuum tube in which no feed-back is employed and may therefore represent the amplification curve oftube 4 with resistance 20 equal to thereby providing ashortcireuit for wind-' 19. Curve 23 represents the amplification curve such as the tube 4 ma have when the feed-back connection .is empl oyed in ac 'cordance with this invention. In one case where the value of resistance 20 was 2500 ohms, the ratio of output current to input current was 40 for the peak of the curve 23 which represented frequencies of the order of 400 to 600 cycles. Heretofore feed-back ,am lifiers have had amplification curves causes an enormous increase over a considthe tu the outgoing line 31'.

erable range of frequencies in the amount of am lification thatmaybe secured from be. The degree of uniformity with which curve 23 is increased over curve 22 at various frequencies depends on the' refinement of design of the feed-back transformer and also on the uniformity of impedance of the receiving device to which the output c rcuit of tube 4 is connected. The most uni form characteristic will be obtained when the receiving device presents a simple resistance impedance.

One way in which thefeed-back amplifier may be made to work into a. receiving device of uniform impedance is to associate the output circuit of the feed-back amplifier with the input circuit of a second am lifier. Such an arrangement is shown in ig. 3 where transformer 16 has its secondary winding connected in the input circuit of an amplifier which is located between tube 4 and The input im edance of tube 30 as seen from the input 0 transformer 16 closely approximates a simple resistance impedance of constant value due to the presence of the resistance element 25 in shunt to the secondary windin of transformer 16. A substantially umform char-4 ,acteristic will therefore be obtained over a wider range of frequencies by the use of the transformer having a plurality of windings,

one of the windings of said second transformer being in said output circuit, another of the windings of said second transformer being in said input circuit, and means comprisin a resistance in shunt to the winding of sai second transformer in said input circuit of such value as to limit the amount of energy transferred through said second transformer suficientl to prevent the generation of omillations by said tube.

2. In an electric system, a vacuum tube having an input circuit and an output circuit, means for supplyin to said input circuit currents t( be amplifi ed, means comprising a transformer for feeding back to said input circuit a portion of the amplified currents in said output circuit, and an adjustable resistance in shunt to a winding of said transformer, sa d resistance being adjusted to a value just below the critical value which will roduce singing.

3. an electric system, a vacuum tube having an input circuitand an output circuit, a transformer havin a winding in said output. circuit and a win%ing in sald input circuit, and means for giving said transformer a substantially uniform translating efficiency over a broad range. of frequencies simultaneously transmitted through said tube, while preventing said tube from generating sustained oscillations.

4. In an electric system, a vacuum tube having an input circuit and an output circuit, a: transformer having a winding in said output circuit and a winding in said input circuit and means comprising a resistance in circuit with a winding of said transformer for making the translating efiiciency of said transformer substantially uniform over a broad range of frequencies simultaneously transmitted through said tube, while re venting said tube from generating sustained oscillations.

5. in an electric system, a vacuum tube having an input an source of waves applied to said input circuit, coupling means for energy, corres ondingin frequency to sai waves, fi'om sai output circuit hack to said input circuit less than the amount necessary to gen erate sustained oscillations, and a sewnd vacuum tube having its input circuit amociated with the output circuit of said first mentioned tube, said input circuit of said an output circuit, a

second vacuum tube being designed to have a substantially pure resistive impwance.

6.linanelectricsystem,avacumwhe having an inputcircuit and an output circuit, a transformer for transferring enerw from said output circuit to said input circuit; and means for causing the impedance of said input circuit as viewed from said output circuit through said transformer to approximate a pure resistance over a wide range of frequencies, while preventing said tubes from generating sustained oscillations.

7; "In 'an electric system, a vacuum tube having an input circuit and an output circuit, means comprising a translator of Imiform .efiiciency over a wide range of frequcncies for transferring ener from said output circuit to said input circuit, and l resistance in shunt to a portion of'said translater, said being of 'such valueth'at the combination ofsaid translator and said resistance amount 0 range of uencies. v

8. In an e tric system, a vacuum tube amplifier having an input circuit and an output circuit, a. transformel 'for transferring energy from saidoutput circuit to said inputcircuit, and a resistance in shunt to a winding of said transformer ofsuch a value as toprevent said tube from ingsustained J 9. In combination a feed backam hfier comprising meansfor producing a su umforrg .actio'n goverr a rou range 0 uencies, an outgoing me having'animpedance-v with fre quency, and means between amphfier andsaid' line for preventing sud line of variable from distorting feed babkhfie'amp cation characteristic of and amr.

feed-back action over a wide 10. In combination-an amplifier in means for producing a feed back action from its output circuit to its input cir-' cuit too weallrihto ltlzaus'e sustamgdoscillation,

an on e avm an m anceva ing an means between sa l d am lifier an sai line-for ca said ampli er to amp independently o the vari-'- able characteristic bf said line.

11. In combination a feed back amphfler rovides a substantially uniform and means for causi 1919. having an output circuit and an inputcir-X e w a d s p e t output circuit and having' an approximating a pure resistance.

12. In .combmation, a feed fier having an input circuit and an output circuit an means, for producin a feed-back 'actioiffrcm its output circuit to its in ut .circuit too weak to cause sustained osc' tion, an outgoing line, a transformer having a winding in said out ut circuit, and a, win 'in mid line, an shunt to the winding of said transformer in 18. In combination a feed back amplifier having input terminais and output terminals a substantially uniform amount of f broad range of frequencies, a receiving 'device, connections between saidoutput terminals and said device, and a shunt to said connections. A a

14.111 combination a vacuum tube ampliresistance fier having an input circuit and an out ut I circuit, a transformer of high mutual 1mpedanceand low shunt capacity for feeding ack into said input circuit a portion of the energy in said output circuit, and a resist-, ance in shunt to a winding of said trans former, said resistance being of such value as to prevent said tube from generating oscillations. f

In witness whereof, I hereunto subscribe my 8rd day of November, A. D.

BERT C.

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